This invention relates generally to the protection of submersible motors that are utilized in systems, such as electric submersible pumping systems, that are submersed in a fluid during operation.
A variety of systems are used in the production of fluid from subterranean locations, tanks and other structures that compel the use of submersible systems. For example, a variety of electric submersible pumping systems are used in wellbores to pump petroleum-based fluids.
In a typical system, a pump is powered by a submersible motor. A motor protector is coupled to the submersible motor to allow for pressure equalization between the interior of the motor and the exterior. For example, if the system is utilized deep within a wellbore, the pressure acting on the interior of the motor must be allowed to substantially equalize with the increasing external pressure incurred as the system is moved deeper into the wellbore. Conventional motor protectors utilize labyrinths, isolation chambers, expandable bags and other types of barriers that permit equalization of pressure without allowing external fluid to move into the motor. Thus, the motor is allowed to undergo pressure equalization without contamination of its internal lubricating oil
Apart from the motor protector, other potential avenues for entry of external fluids into the motor interior are blocked by seals. For example, a power cable typically is routed through an external housing of the motor to provide power to the motor. The power cable is routed through a connector that is securely sealed to the motor housing. Typically, elastomeric seals are used to facilitate sealing of these and other connections. However, elastomeric seals are susceptible to pressure differentials as well as to certain of the corrosive elements often found in locations wherein submersible pumping systems are utilized.
The present invention addresses these and other drawbacks of current systems.
The present invention relates generally to a motor protection technique. The technique utilizes a motor protector having a free flow path from an upper region of the motor protector to the interior of the submersible motor. Thus, a lubricating liquid may be placed inside the motor protector and allowed to freely flow into and throughout the interior of the submersible motor. The system obviates the need for complex obstructions or flow inhibiting passageways that prevent movement of external fluids to the interior of the submersible motor. A common fluid deployed within both the motor protector and the submersible motor is designed to prevent mixing or migration of the wellbore fluid through the motor protector to the submersible motor.
According to another aspect of the present invention, a power cable connector is coupled to the submersible motor to permit electrical coupling of a power cable to the motor. The power cable connector comprises a flow passage that permits the flow of liquid between motor protector, submersible motor and power cable connector. In one embodiment, the power cable connector comprises an isolation tube that extends along the motor protector. Although both the motor protector and the isolation tube are exposed to the external environment, the lubricating liquid disposed within prevents migration of environmental fluids to the interior of the submersible motor.